Telephone-exchange system



G. THOMPSON TELEPHONE EXCHANGE SY STM March Z4, 1925.l

2 Sheets-Sheet 1 /m/enfar. l @ear e /omson lll' Patented Mar. 24, 1925.

unirsi) STATES APii'inur orifice.

o-noneia rnoiirrson, 0F Arazon-nr VnnNoN, New Yorin, assrenon fro Wnsinnn uitno- TRC COMPANY, INCORPDRTED, OF'NEW YORK, N. A CRPEATION Ol? NEW.

YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application led February 9, 192s. Serial No.y 691,557.

To all whom it may concer/it:

Be it known that l, @noi-ion THOMPSON, a citizen of the United States of. America, residing at Mount Vernon, in the county of `lllestchester and State of New York, have invented certain new and useful Improve-- ments in Teleplioneflxchange Systems, of which the following is a full, clear, concise, and exact description. i

This invention relates to telephone ex-v changek systems and more particularly to systems in which connections are established by means of automatic switches.

Telephone systems employing automatic switches are so arranged that under normal e conditions it is impossible to connect with a busy line, the final selector, which has access to subscribers lines, being,` caused to test Whether the line is'idle or busy and to re .ease and transmit a signal when the called line is busy.

For various reasons itis `sometimes desirable to permit the operator to connect With line which repeatedly tests busy. This been accomplished in a Variety of Ways, sii-ally by means of what is known as va no test7 lrey'.` In systems in Which final selectors are employed which release under the control of the calling subscriber, the key control method of connecting with a busy line is entirely satisfactory. It has been found however that, in the case of final selectors which await restoration of the called line before releasing, atie-up may result when the operator releases her endof the no-test connection. rlhis tie-up may be between the final selector used in establishingY the normal call and the final selector used no-test, or if the busy line is acalling line, it may be between the district 'selector with which the subscribers line isconnected and the final selector used nO-test. Even where noA tieup occurs, transmission is frequently interfered with. This is, of leoni-se, undesirable.

lt is an object of the present invention to provide improved means for permitting connection to a busy line.

iti feature of the invention lies in the provision of special incomingselectors at an operators positionl for use in establishing` no-test7 connections with a subscribers line.

Another feat-ure of the invention lies in i the provision of means for preventing' the releaselof said vincoming` selectors until the subscribers line is returned to normal.

il. further features of the invention lies in making the above mentioned release preventing means operative regardless of the condition of tliecalled line.

These and other' features of the inventionV will be more clearly understood yfrom a consideration of the following description in connection with the accompanying drawingigs and appended claims.

. ln the drawings, Fig. 1 shows an inooming selector circuit embodying the present invention. A calling subscribers suhstation and the connection of that substation to said incoming` selector through? an operators .position is indica-ted diagrammatically. Y'

:Fig: 2 shows a final selector ofthe type which awaits the restoration l of the called line before releasing.

lt Will be assumedthat a connection has been established between substation 100 nand substation 200 Iby means of line switch 101,

district selector 102, incoming selector 103 and final selector Q01; Suppose now that conversation over this connection continues Vfor a considerable time yand in the meantime, la subscriber located at substation 110 attempts a` connection With substation 200 a number or times, receiving each time a sig'- nal that the Wanted line is busy. This subv scriber: may have reason to feel that this condition is abnormal and he may then con kneet with .anoperators position. by means of line switch 111 and district selector 112 under the control of register sendery 113.

The trunlr leadingl to the operators position ends in acl; 114i Where a signal (not Shown) Will be displayed 'before the operator. The operator answers the call by inserting` a pluga in jack 114: and ascertains what is Wanted. She may attempt connection with the dcsired line and, also receiving a busy signal, will then request of the B operator over an order Wire (not shown) a no-test connection With substation 200. The B Operator ico will assign a no-test trunk terminating at the first or intercepted operators position in jack 116 and appearing at the B operators position in keys 119 and 166. The B operator will then depress assignment key 119, individual to the trunk and will set up the number of the called subscriber on lier keyboard. The operation of assignment key 119 closesla circuit from battery through the winding of' incoming selector sequence switch magnet 120, lower right contact of cam 121, lower contacts of key 119 to ground. Magnet 120 operates iii this circuit and advances the sequence switch to position 2.

In position 2, ground is connected from the right con-tact of k'cam 130, through the outer back contact of relay 125, lower right contact of cani 131 to conductor 129 causing the sender selector to operate :and connect an idle cordless sender with the assigned trunk. Reference may be made to Patent No. 1,403,862 to A. E. lluiidell, granted January 17 1922, for a complete disclosure oi t-h'e `operation oi' rsuch a sender selector and sender `in connection with a cordless or B operators position. VJhen these ope-rations have been completed, ground is vcoinnected to conductor 132, and thence over the lower left contact of cam 133, Ithrough the winding of sequence switch magnet to battery. ltirfaginet 120 yoperates in this circuit and advances the sequence `switch .to position Then the sequence switch reaches position 23/4, ground `is Iconnected over the upper right and lower lett contacts of cam 171 to vconductor 172 to hold the 'selected sender. Y

l/Vheii the intercepted 'operator inserts plug 118 in jack 1116 ka circuit is completed for relay 1.22 and that relay operates. lf the cordless operator l:has not Vdepressed the assignment key and `the 'sequence `switch 'stand-s in :position 1, a circuit is completed from ground yat lthe front 'contact of relay 122,` upper le/'tt'contact of foam 123, lower left contact o-1` cam '1211, lett winding ot' relay 1-25 lto battery. Relay 125'operates and vcloses la circ-uit yfrom ibattery through lamp 126, right contacts oft fcain 127, inner front contact oi' relay 125, lower contacts of cam 128 to ground. Lamp 126 Alights Lto indicate that the trunk has been seized by the intercepted operator. lhen sequence switch 120 leaves position 1 following the depression otassigninent key 119, the above Atraced circuit :tor relay is opened at cam 1.43 yand that relay releases. In position 2 a circuit tor vlamp 126 is closed through the lower contacts of cam 130.4

1n position 3 the circuit toil 'lamp 126 is extended over vthe lower right and upper left contacts lof cam 127 and contact oi: interruptor K to ground. A circuit is also closed from battery vthrough vlamp 134 and the left contacts of 'cani 127 to the contact of interrupter 135 and ground. These operators keyboard in the manner described in the above iden'tiii'ed YPatent No. 1,403,862, and, when registration is completed, ground is connected to conductor 136 completing a fundamental cir-cuit through the upperl right conta-ct ot' cam 123, lower left coiitact of cam 124, left winding of relay 125 to battery. ltelay 125 operates in this Icircuit 'aii'd completes a circuit from battery through the windingA 'of sequence .switch magnet 120, upper left contact of cam 121, outer front contact ot relay 125, lower right Contact or 'cani 130 to ground. Mag net 120 operates in this Icircuit and advances "tlfie vsequence switch to position y5.

`Wlien the sequence switch reaches posi tion 5, the `energizing Icircuit Vpreviously traced toi' relay is opened, ibut relay 125 is held operatedA in Ia looking y'circuit 4closed in position l from battery through the -le'lit winding ot relay 125, upper right and 'lower lel't contact of 'cam 137, inner front `Contact of relay 125,v lower lett and upper rig-lit contacts of cam 1203, conductor fand vthence rto `ground through the step` lpin-,10; relay o-tl the senden In position 5 the `circuit ctaipdfriye magnet 138 is completed from battery, through the winding of @magnet 13S, kright contacts ot' cam 139, outer 'front contact off relay 125, *lower right contact of cam 130 to'ground. Under lthe control oit magnet 13S, xthe brush rod ot selector switch is lmoved lupward in its brush selecting imovement. As the selector brush 'rod *moves upward commutator brush 111-0 engages conducting segments of `iconiinutator strip 1&11 and `a circuit is completed :from battery ltli-rou'tfgh the lett winding of relay 125, the upper right- Jand lower lett contacts of V'cam 137, inner iront contact oi` relay 125, lower lerft contact of cam 123, upper right contact of cani 12st, commutator strip 14:1,1brusli 140, upper right contact ol' cam 112 yto ground. Each time that ya Iconducting segment is engaged by brush 140, this circuit holds relay 125 operated and shunts the stepping relay of the sender inthe well known manner. 'Vlien the stepping `relay has been deenei'gized a number ot times suiiicient to satisfy the setting of the sender, the fundamental circuit above traced is opened and when brush 1410 encounters an linsulating segment of strip 1-11, relay 125 deeiiergizes. The deenergiza-` tion of relay 125 opens Ithe circuit of updri-ve magnet 13S and the selector comes to .rest in position yto trip the selected set of brushes. The deeiiergization of relay 125 CII cani 1li-2 to ground.

also closes a circuit extending from battery through the Winding` o1 sequence switch magnet 120, lower lett contact or" Cain 121, outer back Contact of relay 125, right contact ot Cain 13() Vto ground. Magnet 120 operates and advances the sequence switch into position 6.

ln position G the circuit ot trip magnet 1&3 is closed troni battery, Winding` of that magnet, upper right contact ot' ca1n`142 to ground. The 1fundamental circuit including relay 125 is again completed troni battery through the lett windingl 'ol-'relay 125, lower lett contact ot cani 1211, upper right Contact ot cani 123, conductor 186 and thence through the stepping relay ot' the sender to `ground. Relay 125 operates and locks in a circuit extending 'troni battery through the let't Winding` ot relay 125, upper right and lower lei't contacts of cani 13T, inner iront Contact ot' relay 125, lower lei't and upper' right contacts of cani 123 and thence to ground as above traced. The operation oi' relay 125 closes a circuit trein battery through the Winding ot sequence switch magnet 120, upper lett Contact oft cam 121, outer trent contact of relay 125, lower right contact of cani lill) to battery. Magnet 12() operates in this circuit and ads vances the sequence switch to position 7.

ln position 'l the circuit ot updrive inagnet 13S is again closed troni lmttcry through the winding olf that inagnet,` right contacts ot Cain 139, outer front Contact et relay 125 to ground at the right contact oit earn 130.'

The trip n'iaggnet 1413 is operated at thistinie and the selected set otbrushes will 1ce tripped as the brush rod nieves upward under the control ot updrive magnet 138 in its group selecting operation. its the selector brush rod moves upward, brush 11111 passes over conclueting` segments oicoininutator strip 145 and intermittently closes a circuit lronibattery through the le'lt Winding of relay 125, upper right and lower lett contacts ot cani 137, inner trout contact ot relay 125, lowerv lett contact ot cani 123, upper lett contact oft cain 124-, connnutator strip 1415, brush upper lett contact ot At each closure Aol this circuit the stepping` relay or" the sender is shunted in the Wellv ltnoun manner, and

when the sonder has heen satislied, the

fundamental circuit ahoye traced is opened. Un the engagement ot the nent insulatingjy segment ot' coininutator strip 145 by brush 144, relay 125 deenergizes opening the circuit ot updrive niagnet 138 and ln'inging,` the selector switch to rest on the lowest terminal ol" the selected group. i-dherelease oit relay 125 also closes a circuit troni battery through the Winding' ot sequence switch magnet 120, lower lett rcontact of cani 121, outer bach contact ot relay 125, lower right contact of cani 130 to ground. lilagnet 120 HL-act ot cani 121, outer liront contact of relay 125, lower right contact of cani 139 to ground. liflngnet 120 operates and advances the sequence switch to position 9. llt the first trunk of the group on which the selectorswitch 15() has come to rest is idle, relay 125 Will release as soon as the sequence switch leaves position 2/(ic. lit' the first trunk is busy, ground Will be present on the sleeve terminal thereof and a vcircuit ivill be coinpleted 'tieni battery through the lett Windii "oit relay 125, lower lett contact ot cani 1 s, lower lett contact cani 123, inner liront contact otrelay 125., lower contacts ot cani 1,317., crush 1117, to ground on th"- sleeve terminal oit a busy trunk. Relay 1 sill be Ainaintained energized. lll/hen the sequence switch arrives in position 2, the circuit of magnet 138 is again closed and the selector switch ycontinues upward in its trunk hunting' o1 i llelay 125 is held operated as the lector passes troni trunk to trunlt over a circuiteI-:tending troni battery'through the right winding ot relay 125., upper contacts ot earn 128, conunutator strip 111@ lio, c-,onnnutator brush 149, upper contacts oit cani 139, outer trout contact ot relay 125,

lower right contact olf caro. 130 to ground. llVhen an idle trunk is toundno ground will be present on the sleeve terminal thereof and the circuit through the lett Winding ot relay 125 will beopened; and when coinniutator brush 149 engagesan insulatingl segment ot strip 1d@ the circuit through the rig-ht Winding` of relay '125 all be rered vand that relay will release. The release ot relay 125 opens the circuit of updrive magnet 138 bri ging the selector switch to rest cn the `terninals correspondinu*l to an idle trunlr. The release ot relay 125 closes a-circuit trein battery through the Winding` oit sequence s vitch magnet 120, lower lett contact ot cani .121, outer back coi act t relay 125,'lower right contact ot cani 130, to ground; llflagnet operates and advances the sequenc- 1. itch to position 11 in which position it remains durar; the voperation ot final selector 250. `When the sequence switch reaches position 10, ground connected to sleeve lnush 147 over the upper lett and loWcrrig'ht contacts oi cani 13?', for the lui-pose ot inalring the selected trunk busy to all other selectors.

-When the incoming` selector sequence rswitch reaches position 11 a vfundmental circuit is completed tronrbattery through the right Winding ot relay 203, upper .right Contact ot cani 20s-L, upper lettcontact ot cam 205., over the tip side of the trunk to terminal 151, brush 152, lower ridht and upper lett contacts el cani 153, conductor.

136, and thence through the stepping relay ot the sender to ground, Relay 203 operates .and loclts in a circuit troni battery, through .the right Winding o' that relay, upper lett Contact ot' ca1n'211, right 'front contact ot' Irela-y 203, upper lett Contact ot cani 20a, upper lett Contact ot cain 205, and tl'ien'ce over' the 'fundamental circuit previously traced to ground. The operation ot' relay 203 :closes a circuit ntenuing troni battery, lett winding ot relay 200, lower lett Contact of cain207, lett. front Contact ot relay 203, lower `lett Contact ot earn 208 to ,grour 1l. Relay 200 operates and loclrs in a circuit through the bach cont-act oft. relay .and the lett front Contact ot relay 200 ground on sleeve brush 206- closes a circuit troni battery @through the Winding ot sequence switch magnet 200` lower contacts ot cani 210, right trout oon tact ot relay 200 .to ground. Mag; iet 200 operates and 'advances the sequence switch topos'ition 2. 1

ln position 2 relay 203 is held operated in the above traced locking circuit, and the `circuit ot high speed updriye magnet 2l2 is closed from battery throughthe Winding ot. that magnet, upper right contact ot Acani 213, lett l'ront Contact ot rela-y 203, lower lett contact ot earn 203 to ground. he brush rod of selector 250 is elevated at high speed under the control ot' this magnet in. its brush selecting nioveinent. A circuit is momentarily -eonipl'eted troni lbattery through the right Winding ot relay 203,

upper right lContact of earn 121M r g, Contact ot relay 203, upper let-t contact ot earn 20st, lower right Contact ot earn 205,l

eoinlnutator strip 214;, brush 215, upper lett Contact yot. cani 207, lett 'front Contact ot relay 203, lower lett contact ot Cain 208 to ground `each time brush 215 engages a yconducting segment ot connnutator strip 214-.; This circuit shunt-s the stepping Irelay ot the sender While holding relay 203 operated. l'llhen the stepping relay has .been shunted a sufficient number ot time-sto satisfy the oon-A dition set up in the sender, the tundanientalA circuit is opened. YWhen brush 215 eneoun- `ters the next insulatingseginent ot strip 214, the.- holding circuittor relay 203 is also opened and that relay deenergizes. 203 in releasing opens the circuit .of the up drive magnet and brings selector 250 to rest in position to trip theI selectedset ot brushes. rlie `release of relay 203 .also closes a circuit troni battery through the Winding of sequeneesi'viteh magnet 209, upper right Contact ol cam 210, lett bach contact. of re lay 203, lower lett contact ot cam 208 to The operation ot relay Relayground. Magnet '20.9 operates and advances lthe :sequence switch to position `3.

ln position 3 the circuit yof `trip magnet 219 is closed troni battery through the Winding ot that magnet, lower Irigl-it .contact ot cana 220 .to ground. The fundamental circuit is again closed in position 3 through the right Winding tot relay 203, upper right Contact ot .cani 204, upper lett contact ot vCain 205 and thence to ground through the stepping relay of .the sender. Relay `203 operates :andloclrs :as betere described. lt also .closes .a circuit troni battery vthrough the vinding or sequence `switch ymagnet 209, y upper lait Contact of caniL 216, lett trout' Contact ot relay :203, low-er lett contact of Cain 203 to ground. llaguet 20.9 operates En position 'fl rela-y 203 is held operated in and advances the sequence switch to posit-ion its locking cincarit -Wh-ich extends from `battery through the right Winding thereof, up-

aiaght. Contact ot can1;211, right trent contact `ol' vrelay 203., upper lett Contact of earn 20a, `upper lett Contact ot Cain 205 and thence over the vit'undaniental circuit as ypretact ot cani 20??, lett trout :contact ot relay 203,10We-r le'lteontaot etica-111203 to ground each time brush .213 encounters Va iconducting segment :ot strip 217. rlhe Stopping relay `ot the sender `is intermittently ,shunted and when this has been done :a sutticient niunber ,ot tiniesthe fundamental 4circuit is opened. Then brush 218 engages the next iusul-atingsegment 4in :strip 217, the holding circuit of relay 203 is opened and that relay deenergizes. lay 203 opens the circuitot updrive magnet 212, and brings the lselectoryto rest with the brushes engaging the first terminals ot rthe .selected group. The release of relay 203 also closes a circuitr trom battery, winding ot sequence switch magnet 209, upper right Contact ot'oani 210, lettfbaclz Contact otrelay 203, lower ylett Contact ot cani 200 to ground, Magnet 209 operates and advances the sequence switch toposition 5.

ln posit-ion 5 Athe `fundamenta-l circuit. isl

again closed through the right Winding ot relay 203, upper right contact oteani 201.2, upper lett Contact ot cam 205 and thence. as previously traced through the stepping relay ot the sender to ground.V Relay '203 operates and locks ras before described, -olos- The Ideene-rgization ot` re- `ing a circuit from battery through the winding ot magnet 209, upper lett contact ot cam 216, lett front contact of relay 203, lower lett Contact ot cani 203 to ground. Magnet 209 operates and advances the sequence switch to position 6. Relay 203 is held operated in position 6 in a circuit extending through the right winding ot relay 203, upper right contact of cam 211, right front contact of relay 203, upper lett cont-act ot cam a and thence as previously' traced to ground in thesender.

In position 6 the circuit ot' low speed updrive magnet 221 is closed from battery through the winding thereof, upper right `contact ot cam 207, lett front contact of relay 203, lower lett contact of cam 208, to

Y ground. The selector switch 250 is advanced has taken place a sutlicient number of times,

the fundamental circuit is opened. When `brush 215 engages the next insulating segment ot strip 21e the holding circuit ot relay 203 is opened and that relay deenergizes.

rltlhe deenergization of relay 203 opens the circuit ot updriye magnet 221, bringing J. 1 1 1 the b1 ash set to rest engaging tie termina s ot the wanted line.V The release ot relay 203 closes a circuit trom battery through se- ;quence switch magnet 209, upper right contact of cam 216, lett back contact ot relay 203, lower lett Contact ot cam 208 to ground. Magnet 209 operates and advances the sequence switch to position'9.

`When the final selector sequence switch reaches position 6554i, a circuit is completed trom battery through low resistance 154, lower right contact of cam 155, brush 156, terminal 157, upper contacts ot cam 222, winding ot relay 223 to ground. Relay 223, operates opening the locking circuit of relay 206 which releases. Vith relay 206 released, when the final selector Vsequence switch arrives in position 9, a circuit is completed from, battery, through the winding ot sequence switch magnet 209, lower right and upper lett contacts ot cam 210, right back contact of relay 206, to ground. y1Viagnet 209 operates and advances the sequence switch to position 13 without testing whether the called line is busy. y

As soon as units selection is completed, ground is connected to conductor 132, and thence over the lower left contact of cam 133, through the winding of incoming selector s-equence switch magnet 120, to battery.l litagnet 120 operates and advances the incoming selector `sequence switch to position 12. li/Vhen the sequence switch leaves position 11 ground is disconnected trom conductor 172 at the lower lett Contact of cam 171, releasing the sender. 1t the intercepted operator has seized the trunlf; and relay -122 is operated, a circuit is completed, in position 12 oi the incoming selector sequence switch, extending from battery through the left winding of relay 125, lower left contact of cam 124, upper lett contact of cam 123, front Contact of relay 122 to ground. Relay 125 is operated and closes a circuit :froml battery through the vwinding of sequence switch magnet 120, upper lett contact of l -cam 121, outer front Contact of relay 125,

lower right contact ot cam 130`to ground vMagnet 120 operates and advances the 1nconnng selector sequence switch to position 14, As soon as the sequence switch reaches position 13 a locking circuit is completed 'for relay 125 from battery through the lett winding of that relay, lower lett contact of cam 1241, lower right contact of cam 123,

pendent ot relay 122.

In position 13 of the nal selector sequence switch relay 206 is againy operated in a circuit extending from battery through the lett winding of that relay, upper left Contact of cam 220 to ground. Relay 206 operates and, since relay 223 released when the sequence switch lett position 8%, locks as before to ground on sleeve brush 147. The operation of relay 206 also closes a cirn cuit trom battery through the winding of sequence switch magnet f209, lower contacts ot cam 210,A right front contact of relay 206 to ground. Magnet 209 operates and advances the linal selector sequence switch into position 14:. Since relay 203 isnot operated at this time ja circuit is closed` from battery through the winding of magnet 209, upper right contact ot' cam 216, lett back contact of relay 203, lower left contact of cam 208 to ground. Magnet 209 operates and advances the sequence switch to positionr15. With the incoming selector se quence switch standing in position 111 and the nal selector sequence switch standing in position 15 a talking circuit is completed trom the intercepted operators headset (not shown) associated with cord circuit 115, tip ot plug 113 and jack-116, throughcondenser 117, 'lower contacts of cam 153,`brush 152, terminal 151, upper contactsfot cam 205, final selector brush 225, multiple terminal 226 over the called subscribers linev tact of cam`155, condenser 177, ring of jack 116 and plug 113 to the operators headset. v

`to ground, thus rendering relay 125,indey I 'station 260y is restorcdto normal.

" batter f t-hroueh: the right Windine of' rela LJ di 2D 158, Winding of relay:159yrightbaclr contact ofrelay 158, upper contact of interrupter 170', lower lettafnd upper right `contacts of cani 160, back contact off relay 122 .to gOUIld. Rel-ay 159 operates,- butthe current-flowing through the:` right Winding of relay 158 is not sufficient to cause that rela-y to operate. Relay 159 in operating connects ground to the lett side-ot the Winding ot relays 161 and 162.

Under the assumption niaoe that substation- 200' Wasfbusy on aI ca v-iincoming from substation 160, battery Willhe supplied to substation 260 troni incomingselector 1623. Relays` 16,1 and 162 have a; high resistance and are sov adjusted as to be very sensi-tive. They Will therefore operate under practicallyall the current conditions that'exist at subscribers line termin-als throughout the establishment ot a call, and without causing suilicient current drain to interfere with the establishment ot such call or 'with tir gress of conversation. Under the assumed condition a circuit will be completed trein battery at selector 163-3 `over brush 163, terininal 1641, brush 232E multiple terminal- 230, multiple terniiinal brush upper contacts of caniV 229-, terminal 157j brush 156, uppei1 lett contact ot carn- 155, Windingol' relay1-62 toy gro-und at tlie outer right coutact ot' relay Relay 162 operates and closes its left'contact. ln sonic ycases when a substation is busy with an originating call, with dialing in progress, battery is connected to the tip side of the line, in Which case if connection is established thereto troni an incoming selector such vas 150, relay 16.1 wouldk be operated. The purpose ot having two relays is to insure the operation of this delay ineans, irrespective of the side of the line to which battery is being sup-plied 1n the case of coin battery, which is sometimes supplied toboth sides ot the line at once, both relays would operate. e

l/Vhen relay 159 operates it also closes a locking circuit for itself exteuci'ngtrom battery throughl the right lWinding of relay 158, Winding ot' relay 159, left Winding of relay 158, letfront contactot relay 1.59, lower left and upper right contacts of cam 160,

back contact ,of relay 122 to ground.. ils long'asinterrupter 170 holds its upper contact closed a portion otthe original energizing circuit of relay 159 shunts the lett Winding of relay 158 and that relay remains deenergized. However, when interruptor 170 Opensits upper contact, the current flowing in bothwindings oi'y relay loo causes it to attract its armatures. llela-yvvll in operating closes a second ground connection to the left terminals of the Wind-ings or rclays 161 and 162. lllffheninterrupter 170 closes its lower contact,a circuit is coinpl'eted' frein' battery' through the right Windingiot relay 158, front Contact ot relay 162, (orrr 161 that relay had been energized),

lower contact' et interrupter 176, lower ler't and upper right contacts otcain 160 to.

ground atr therba'clr Contact ot relay 122. rlhis circuit shunts the Winding or' relay 159 and that relay dfecnergiZes, but the circuit otrelay maintained troni the arniavture relay 158. .ll/27 hen 'interrupter 170 opens its lower contact, the circuit of relay 158 is 4opened and thatrelay deenergizes, opening the circuit Vot relay 162. lWhen interl-npter. 170 aga-in: closes its upper contact the vcircuit previously traced for relay 159 is completed and the cycle of operation justy outlined i-srep-cated;

Wheuz thesubscriber at substation 200 restores' his 'receiver and releases the connectionmover' incoming selector k103 and inal selectorl 201, battery is reniove'( troni tcrininal 227 and relay 1622 releases. W ith relay 162` releaseda when interrupter 170 closes its louter contact,y the circuit previous-ly traced. tor-relay 158, in shunt of relay 159, is opened at the contacts ot' relays 161 and 162, and the loclringcircuit for relays 15S und 159 is maintained. l.Vith relays 158 and' 159 opel1- ated, When interrupter 17() again closes its upperI Contact, a circuit may be'traced troni battery throughfthev ivindingfott incoming selector sequencevv switch niagnetn126, lower right contact of cani 121,. left Jfront coiurutt ot"` relay 158, upperl contact ot intcrrupter H6, lower left and upper right contacts ot cam 160', back contact ot relay 122 to ground. Magnet 120 operates in this circuit and advances the sequence switch to position 16. Vhen the sequence switch leaves position 141/14, relay 125 releases and a circuit is closed from battery through lamp 126,- lower lett contact of cam 136` outer back contactot relay 125, lower left contact of cani 131, contact of interrupter 165 tol ground. il circuitlis also completed from battery through lainp- 134, lower lettand upper right cony tacts vof cani 127, inner bach contractor relay 125, lett contacts of cam 131, contact or" interrupter 165 to ground. Lamps k134 and 126 flash in these circuitsuntil the tru-nk is returned to normal. The operator observingthetlashi-ng of lamps 134 and 126, de-

Apresses key 166, completing;` a circuit from battery through the .winding of sequence switch 120, lower right contact of cam 133, contact of ley 166 to ground. Magnet 120 operates and Vadvances the sequence switch to position 18.

ln position 18 a circuit is completed from battery, windingof downdrive magnet 167, lower Contact ot' cam 142, to ground. Under the control ot the downdrive magnet, selector switch 150 is restored to normal. Upon reaching normal position, brush 144 encounters connnutator segment 168 and a circuit is completed from battery through the winding, ot sequence switch magnet 120, upper right contact of cam 121, segment 168, brush ,144, upper left contact of cam 142 to ground. lllagnet 120 operates in this circuit, restores the incoming` selector sequence switch to normal and extinguishes lamps 134 and 126.

lllhen the incoming; selector sequence switch leaves position 161Ar ground is renior'ed trom sleeve brush 147 and the circuit et relay 206 is opened. Relay 206 in releasing closes ,around to terminal 146 from the upper right contact of cam 224 over the left back contact ot `relay 206, to hold the trunk busy until the final selector has been restored to normal. Thev release of relay 206 closes a circuit from battery, through the lett windingr ot relay 203, upper contacts ot cam 21,0, i" t back contact ot' relay 206 to `ground. .ll-.clay 206 operates and closes a circuit from batterjjf through the winding of final selector sequence switch magnet 209, upper lett contact of cani 216, lett front contact of relay 203, lower lett contact of cam 208, to ground. Magnet 209 operates and advances the se# quence switch to position 16. Since the subscriber has already restored his receiver to the switch-hook, the circuit of relay 203 is opened when the squence switch reaches position 1",` and that relay releases, closing a circuit troni` battery tl'irough the winding of sequence switch magnet 209, upper right contact ot cam 216, lett back contact of relay 203, lower lett contact of cam 208 to `ground.. Magnet 209 operates and advances the squence switch to position 17. j

.lu position 17 a circuit is closed from battery through the winding:A of sequence switch magnet 209, lower right and upper left contact ot cani 210, right back contact of relay 206 to ground. Magnet 209 operates and advances the sequence switch to position 18.

ln position 18 the circuit of the downdrive magnet is closed from battery, winding" of magnet 236, lower contact of cam 213, upper left contact ot cam 207, lower left contact of cani 220, to ground. Under the control of magnet 236, selector 250 is restored to normal whereupon a circuit is closed from ,batt-ery, through sequence switch magnet 209, lower right contact of cam 216, eommutator segment 247 brush 218 lower `left contact ot cani 220 to ground. Magnet 209 operates and advances the sequence switch to position 1, whereupon the final selector is in condition fory use with other calls.

ln case substation 200 had been busy as a called line and the final selector' is still connected thereto and awaiting` the restoration of the switchhook, conditions are s0Inewhat different. lt will be remembered that upon the release ot the final selector by the incoming selector, 'relay 206 deenergizes closing` a circuit for relay 203 extending` from battery through the lett winding ot that relay, upper contacts of cam 210, to `around at the right back Contact of relay 206. The energization ct relay 203 causes' the 'r-idvance of the final selector sequence switch to position 16. Assuming that a final selector similar to selector' 250 has been used yin the establishment ot a normal call, and

the line oi' the called subscriber has not been restored, a circuit will be established in position 153A1 extending troni battery through the right winding` ot relay 203, upper contact of cam 211, right iront contact of relay 2053, lower lett and upper' right contacts oit cam 229,` brush 228, terminal 227, over the subscriber"s loop bach to terminal 226,`brush 225, upper right contactl of cam 205, lower lelft contact oit cam; 204 to ground, which wi ll hold relay 203 energized while the subferilli/.ifs receiver remains oil the switchhoolq.

L over the upper Contact off'caui 235 is r nectcd in parallel with the windingv ot rela, 203. ll" the final selector used no-test" should be connectedwith a subscribersline under these circu instances, and the resistance of the line loop is quite low. insulli yient current r hes relay 162 to cause it tooperatc. Relays 'Si and 150 remain locked and whenv interrupter 170 closes its upper contact'. a second time a circuit is closed for sequence switch magnet 120 extending' fro-in battery' through the windingl of magnet 120, lower rigight contact ot cani 121, riwht 'trout contact oi'5 relay 156, upper Contact ot interruptor 170, lower lett and upper right contacts ot cam 160, bach contact of relay 122 to ground. llrlapgnet 120 operates in' this circuit and advances the incoming selector sequence switch to position 1 6. When the sequence switch reachesposition 143/, a circuit is completed troin lmttcry, right winding` ot relay 125,

lower richt and uo ver le'lit contacts of Cain` 160. lower contacts oit ca1n`153, brush 152, terinminal 151, upper contacts ot'` cam 205 ol the `final selector sequence switch used no-test which isstanding in talking position, that is, position 15, brush 225, 'terminal 226, terminal L38, brush 237, and thence over the upper right contact ot a cam correspondinf; to'cam 205 and the lower lett contact ot a cam corresponding to cam 204, belonging to the final selector which is awaiting resto Vln Vposition 16 battery tlirougrh resistance switch ot the iinal selector which Was aivaiting' release to advance out ot position 16.

Upon leaving; position 1G ground is disconnected from multiple terminal 226 and the circuitpreviously traced-.tor relay 125 i opened, whereupon relay releases closin..` the circuits ot lamps 126 and to display the disconnect signal, after which the operation is the same as previously described. lt the loop circuit is ot sutliciently hioli resistance, relay 162 Will receive enough current to operate and the holding;` operation Will be as is described. n.

It, when the incoming selector 253() hunts for an idle hnal selector, which takes place in position 9 there should be none available 'the selector comes to reston a set ot overflow terminals the sleeve of which is not connected to ground and hence relay 125 releases. '.lhe release ot relay 125 closes a circuit v.extending` from battery through the Winding ot sequence switch magnet 120, lower lei-'t contact of cam- 121, outer baclf` contact of relay 125, lower richt contact ot cam'130 to ground. Magnet 120 operates and advances the sequence switch into position 11.

1n position 11 a circuit is closed for lamp 13d extending` from battery through the lett contact ot` cam 12?', contact of interrupter 135 to ground, in Which circuit lamp 135 flashes. The operator noting` the flashing ot' lamp 134 alone, depresses the c isconncct l-ey 166, closing` circuit from battery through the Winding; ot sequence switch magnet 120. loiver right contact ot cani 13S, contact ot ley 166 to ground. lilagnet 120 operates in this circuit and advances the sequence switch to position 1&1. Meanwhile a signal has been transmitted to the intercepted operator and she Will remove plug; 118 from jack 11G, releasing' relay 122.' The release ot relay 122 initiates the operation of relays 158 and 159 and since no final selector has been seized, and relays 161 and not operated. as soon as interrupter 170 closes its circuit the .second time. the circuit previously traced ttor magnet. 120 is closed and the sequence switch advanced to posit-ion 16.

ln position .16. since relay 123 is not operated. the-circuits ot lamps 131- are closed as before described and hotl. lamps Yash after which the operator can depress key 166 and release progresses as previously described. The operator may hold lrey 1G13 depressed until both lamps Hash, thus avoiding the second depression ot the disconnect key.

One lof the difficulties which this schemev is designed to overcome is the destruction oit transmission when a final selector used 1o-test is lett in position awaiting,` the restoration of the subscribers switchhookv during' the time that a conversation is in progress. This may be pointed out in the drawing of the final selector shovvn in Fig. 2. 1n position .16, When the subscribc-rs receiver is oit the switchhool, battery through the right Winding` ot relay 203 and battery through resistance 234i, are connected in parallel-to the ring side ot the subscribers linefivhich is the same side to which batt-ery is being` supplied from the incoming selector on the completed con.- ncction. These batteries would oppose one another and would greatly reduce or possibly destroy transmission. incoming selectorr ot' the present invention it is impossible to advance the final selector used fno-test until after the subscribers switchhool has been restored, this diiiiculty has been entirely overcome.

rlrnothcr advantage of the present invention lies in the provision ot condensers 117 and 17T. Which prevent the transmission ot battery trom the intercepted operators cord circuit to the terminals of the called line which might also `interfere with transmission on a call in progress.

Another source of diiiiculty overcome by the present invention arose in central offices Where reversed ringing current for party line iiiiigriira,` Was provided by reversing the connection ot the line to the multiple terminals in. the 'final selector terminal bank.

Under this condition, it was possible for a final selector used no-test and one usedv tor a normal call to both arrive at the position ot awaiting;` the release ot the called line at the vsame time but on the terminals ot ditterent parties so .as to be reversed with respect to one another. This would result in a pair ,otcircuits from the relays 20:3 otzeach tinal selector circuit to ground at the lower lett contact ot cam4 204 of the other circuit independent of' the called line, whereupon neither final selector could release until artificially released by an attendant. Preventing` the release ot the incominn'lselector used no-test7 until the called line is restored entirely overcomes this ditficulty. i

l/Vhat is claimedy is:

l. ln a telephone exchange system, sul)- scribers lines, automatic switches for establishing` cimnections `between' said lines, means :tor rendering" said connected lines non-selectable to said automatic switches,

another automatic switch, control circuitsr therefor, means inV said control circuits for establishing` connection over said last mentioned automatic Switch with a line which has been rendered non-selectable and means tor delayingrthe release oztsaidlast men- Since with the tioned automatic switch until said line has been opened.

2. In a telephone exchange system, subscribers lines, automatic switches for establishing connections between said. lines, means for rendering said connected lines non-selectable to said automatic switches, another automatic switch, control kcircuits therefor, means in said control circuits for establishing connections over said last mentioned automatic switch with a line which has been rendered non-selectable, operator controlled means for releasing said automatic switch and means for preventing the release of said automatic switch until said line has been opened.

3. In a telephone exchange system, subscribers lines, automatic switches for establishng connections between said lines,

means for rendering said connected lines non-selectable to said automatic switches, another automatic switch, control circuits therefor, means in said control circuits for establishing connections over said lastv mentioned automatic switch with a line which has been rendered non-selectable, an operators position, means at said operators position for releasing said automatic switch,l a signal at said operatorsposition, means responsive to the opening of said subscribers line for displaying said signal and means for preventing the release of said automatic switch until said signal has been displayed.

In witness whereof, I hereunto subscribe my name this 5th day of February A. D.,

GEORGE THoMPsoN. 

